Symptomatic patients with aortic stenosis exhibit abnormal ventricular function during exercise. Using radionuclide angiography, we studied left ventricular systolic and diastolic performance in 11 asymptomatic patients with isolated aortic stenosis (rest gradient by continuous wave Doppler 64+-31 mmHg, range 40-144 mmHg) and left ventricular hypertrophy by echo. Patients were compared to 12 aged and gender-matched normal volunteers. Changes from rest to exercise ejection fraction, stroke volume, cardiac output, and end-diastolic and end-systolic volumes were quantified for each group. Peak diastolic filling rate at rest was reduced in patients with aortic stenosis compared to normals. During supine bicycle exercise, patients with asymptomatic aortic stenosis demonstrated significantly less of an increase in left ventricular ejection fraction during supine exercise. This was associated with less of an increase in cardiac output and actual falls in stroke volume and end-diastolic volume during exercise compared to increases in these parameters in the normal volunteers. Thus, abnormal left ventricular systolic and diastolic function limits the cardiac output response to exercise, resulting in effort limitation in patients with aortic stenosis, even when clinically asymptomatic.